Zafi.B and Netsky.P have managed to notch up another month on top of the chart for the worst malware mischief-making.

According to infections reported to antivirus firm Sophos during October, Netksy.P -- first sighted in March of this year -- has taken the top spot with over 35 percent of infections and Zafi-B -- first spotted in June -- follows up in second place with 28 per cent.

Both viruses have stayed in the top 10 since they first surfaced in the wild, although Zafi.B had been leading the virus pack until this month.

Netsky.P spreads via email by harvesting addresses from local drives. The virus saves itself to peer-to-peer shared networks with a variety of filenames, including supposed references to sexual antics of pop stars including Britney Spears and Eminem; Harry Potter; software cracks; the Atkins diet; and others.

With numerous versions of the Netsky virus available in the wild, Graham Cluley, senior technology consultant at Sophos, said it was difficult to see why the P variant was so successful.

"I believe it simply reached a critical mass earlier than other versions, and has successfully managed to embed itself on computers which are failing to be secured with the latest antivirus updates," he said.